LTE, or Long Term Evolution, refers to research and development involving the Third Generation Partnership Project (3GPP), to identify technologies and capabilities that can improve systems such as the UMTS. A current working assumption for LTE is that users are explicitly scheduled on a shared channel every transmission time interval (TTI) by an eNodeB (eNB). An eNodeB is an evolved Node B or E-UTRAN Node B and is the UMTS LTE counterpart to the term “base station” in the Global System for Mobile Communication (GSM).
As can be seen in FIG. 1, the UMTS architecture consists of user equipment 102 (UE), the UMTS Terrestrial Radio Access Network 104 (UTRAN), and the Core Network 126 (CN). The air interface between the UTRAN and the UE is called Uu, and the interface between the UTRAN and the Core Network is called Iu.
The UTRAN consists of a set of Radio Network Subsystems 128 (RNS), each of which has geographic coverage of a number of cells 110 (C), as can be seen in FIG. 1.
The interface between the subsystems is called lur.
Each Radio Network Subsystem 128 (RNS) includes a Radio Network Controller 112 (RNC) and at least one Node B 114, each Node B having geographic coverage of at least one cell 110. As can be seen from FIG. 1, the interface between an RNC 112 and a Node B 114 is called Iub, and the Iub is hard-wired rather than being an air interface. For any Node B 114 there is only one RNC 112. A Node B 114 is responsible for radio transmission and reception to and from the UE 102 (Node B antennas can typically be seen atop towers or preferably at less visible locations). The RNC 112 has overall control of the logical resources of each Node B 114 within the RNS 128, and the RNC 112 is also responsible for handover decisions which entail switching a call from one cell to another or between radio channels in the same cell.
E-UTRAN is a packet-data-based transmission system. It is required to be in coexistence with 3GPP Radio Access Technology (RAT). The Radio Access Technology is the air interface that is used to allow the link between the end user equipment and the Access Point or Base Station of Radio Access Network (RAN). In particular, E-UTRAN should be in coexistence in the same geographical area and co-location with GSM/EDGE Radio Access Network (GERAN) on adjacent channels. E-UTRAN terminals supporting UTRAN and/or GERAN operation should be able to support measurement for handover between different 3GPP RATs. In E-UTRAN, different carrier frequencies are expected to be used simultaneously. Thus, in additional to intra-frequency measurements, inter-frequency measurements are also necessary to enable inter-frequency handover.
Generally speaking, a prefix of the letter “E” in upper or lower case signifies LTE, although this rule may have exceptions. The E-UTRAN consists of eNBs (E-UTRAN Node B), providing the E-UTRA user plane (RLC/MAC/PHY) and control plane (RRC) protocol terminations towards the UE. The eNBs interface to the access gateway (aGW) via the S1, and are inter-connected via the X2.
An example of the E-UTRAN architecture is illustrated in FIG. 2. This example of E-UTRAN consists of eNBs, providing the E-UTRA user plane (RLC/MAC/PHY) and control plane (RRC) protocol terminations towards the UE. The eNBs are interconnected with each other by means of the X2 interface. The eNBs are also connected by means of the S1 interface to the EPC (evolved packet core) more specifically to the MME (mobility management entity) and the UPE (user plane entity). The S1 interface supports a many-to-many relation between MMEs/UPEs and eNBs. The S1 interface supports a functional split between the MME and the UPE. The MMU/UPE in the example of FIG. 2 is one option for the access gateway (aGW).
In the example of FIG. 2, there exists an X2 interface between the eNBs that need to communicate with each other. For exceptional cases (e.g. inter-PLMN handover), LTE_ACTIVE inter-eNB mobility is supported by means of MME/UPE relocation via the S1 interface.
The eNB may host functions such as radio resource management (radio bearer control, radio admission control, connection mobility control, dynamic allocation of resources to UEs in both uplink and downlink), selection of a mobility management entity (MME) at UE attachment, routing of user plane data towards the user plane entity (UPE), scheduling and transmission of paging messages (originated from the MME), scheduling and transmission of broadcast information (originated from the MME or O&M), and measurement and measurement reporting configuration for mobility and scheduling. The MME/UPE may host functions such as the following: distribution of paging messages to the eNBs, security control, IP header compression and encryption of user data streams; termination of U-plane packets for paging reasons; switching of U-plane for support of UE mobility, idle state mobility control, SAE bearer control, and ciphering and integrity protection of NAS signaling.
E-UTRAN supports intra-frequency (serving frequency layer), inter-frequency (non-serving frequency layer) and intra-RAT handovers. Typically, UE (user equipment) measures the power, or some other measurement quantity of Pilot channel or reference signal channel of different cells periodically. If the measurement results between the current serving cell and a neighboring cell satisfy some criteria, the UE will be handed over to the neighbor cell. The reporting criteria may be periodical or event-triggered.
An example of the UE is a mobile terminal as shown in FIG. 3. The mobile terminal has a transceiver for transmitting and receiving signals in a radio access network. The mobile terminal has a processor to process signals and data. The processed signals or data can be the pilot symbols received from the network. The mobile terminal also has a measurement module for measuring the pilot symbols for handover, for example. The measurement module can also be configured to measure channel quality, for example.
When interference coordination scheme is used, base station will allocate radio resources based on UE's location in a cell (cell center or cell edge). There are various ways to clarify whether the UE is located at the cell edge or at the cell center. For example, geographical distance, pathloss, and geometry (G)-factor can be used to determine the UE's location in a cell. The frequency sub-band allocated to a cell edge user is called a cell edge sub-band, and the frequency sub-band allocated to a cell center users is called a cell center sub-band.
The invention is related to LTE, although the solution of the present invention may also be applicable to present and future systems other than LTE.